1. Field of the Invention
The present invention relates to a musical tone synthesizing apparatus which generates musical tones which ar based on the tone generation mechanism of an acoustic musical instrument.
2. Prior Art
Conventionally, methods of synthesizing the musical tones of an acoustic musical instrument by making a model of the tone generation mechanism of the instrument and simulating this are known. This type of art was disclosed in, for example, Japanese Patent Application, Laid-open publication No. 63-40199, and Japanese Patent Application, second publication, No. 58-58679.
FIG. 2 shows the construction of a musical tone synthesizing apparatus which simulates the tone generation mechanism of a wind instrument as an example of this type of art. In FIG. 2, ROM (Read Only Memory) 11, adder 12, subtracter 13, and multipliers 14 and 15 are shown. These component elements 11-15 comprise excitation circuit 10. This excitation circuit 10 simulates the operation of the mouthpiece and the reed in a wind instrument such as a clarinet or the like.
Bi-directional transmission circuit 20 simulates the transmission characteristics of the resonance tube in the body of a wind instrument. This bi-directional transmission circuit 20 comprises delay circuits D, D. . . , which simulate the propagation delay of the air pressure waves in the resonance tube, junctions JU, JU. . . , which are inserted between these delay circuits, low pass filter LPF, which simulates the loss, etc., of energy at the time of the reflection of the air pressure waves at the end of the resonance tube, and high pass filter HPF, which obstructs the direct current component of the data transmitted within bi-directional transmission circuit 20.
Junctions JU, JU . . . simulate the dispersion of the air pressure waves generated at the points where the diameter of the resonance pipe changes. The junctions JU, JU . . . shown in FIG. 2 use a 4-multiplication lattice comprising multipliers M.sub.1 -M.sub.4 and adder A.sub.1 and A.sub.2. The symbols "1+k", "-k", "1-k", and "k" which are attached to the multipliers M.sub.1 -M.sub.4 are coefficients of multiplication. The value of k in these coefficients of multiplication is so set that transmission characteristics which are almost equivalent to those in an actual resonance tube are obtained.
With the above described construction, the data P which correspond to the pressure which the player puts into the wind instrument are inputted into the adder 12 and the subtracter 13. Furthermore, the data outputted by adder 12 are transmitted within bi-directional transmission circuit 20 in the following manner: delay circuit D.fwdarw. junction JU.fwdarw. delay circuit D.fwdarw. . . . , and reach low pass filter LPF. Next, after passing through low pass filter LPF and high pass filter HPF, the data are transmitted in the opposite direction from the above, from delay circuit D.fwdarw. junction JU .fwdarw. . . . , are outputted from bi-directional transmission circuit 20 and are inputted into subtracter 13. It is here that the data outputted by bi-directional transmission circuit 20 are made to correspond to the pressure of the air pressure waves which return from the end of the resonance tube in a wind instrument to the space between the reed and the mouthpiece.
Next, subtracter 13 subtracts data P from the data outputted by bi-directional transmission circuit 20. By means of this subtraction, data P.sub.1, which correspond to the air pressure in the gap between the reed and the mouthpiece, are obtained. The data P.sub.1 are supplied to ROM 11. ROM 11 outputs data Y, which represent the cross-section of the gap between the reed and the mouthpiece corresponding to data Pl; or which, in other words, correspond to the admittance with respect to the flow of air.
FIG. 3 shows an example of a nonlinear function A which is stored in ROM 11. This nonlinear function A shows the cross-section (output) of the gap between a reed and a mouthpiece corresponding to the air pressure (input) within the gap between the reed and the mouthpiece. Furthermore, data Y, which are outputted from ROM 11, and data P.sub.1 are multiplied by means of multiplier 14. By means of this, the data FL, which correspond to the flow velocity of the air which passes through the space between the reed and the mouthpiece are obtained.
The data FL are multiplied by coefficient of multiplication G by means of multiplier 15. This coefficient of multiplication G is a constant determined in correspondence with the tube diameter in the vicinity of the place where the reed is attached in the wind instrument, and corresponds to the resistance to the air flow, in other words, to the impedance with respect to the air flow. Accordingly, the product of the flow velocity of the air flow which passes through the space between the mouthpiece and the reed and the impedance with regard to the air flow in the tube, in other words, the data P2 which correspond to the component of the change in pressure within the tube which is caused by the air flow passing through the space, is outputted by multiplier 15. Furthermore, these data P2 and data P are added by means of adder 12 and are inputted into bi-directional transmission circuit 20.
In this way, data circulate in the closed loop formed by excitation circuit 10 and bi-directional transmission circuit 20, and resonant operation is achieved. In addition, data are retrieved from the point of connection of the low pass filter LPF of the bi-directional transmission circuit 20 which is in resonant operation, and based on these data musical tones are generated.
However, in the conventional musical tone synthesizing apparatus described above, the amount of time from the input of data P to the stabilization of the resonant operation in the closed loop may be large. In this case, there is a problem in that it takes a great deal of time before a stable musical tone signal can be obtained.
Furthermore, in the loop circuit formed by excitation circuit 10 and bi-directional transmission circuit 20, the resonance characteristics have a number of differing resonance frequencies. If there is no profitable difference in these resonance frequencies, it is unclear at which resonance frequency resonance should be achieved, and it becomes difficult to cause resonance at the desired resonance frequency. Accordingly, in this case, there a problem in that it may not be possible to obtain the musical tone of a desired tone pitch.